Method of making resistance units



Oct. 6, 1936. G. F. MAGDZIARZ METHOD OF MAKING RESISTANCE UNITS Filed May 31, 1950 Patented Oct. 6, 19316 UNITED} STATES" 2.05am unrnon or mama nssrs'rmoa UNITS George F. Magdflan,

Chicago, 111., assignor to Besisteiite Corporation, Chicago, 111., a corporation of Illinois- Application May 31, mo, Serial No. 457,030 9 (Ci. 201-45) I The invention relates generally to units for introducing resistance into electrical circuits and has as its general aim the production of a new and improved resistance unit by a novel, simple,

improved process in which a resistance material,

in the nature of a comminuted substance which has a relatively low electrical conductivity, such as graphite, is first plasticized, then moulded into a desired shape and subsequently removed from the mould in a novel manner in condition for use; or, where desired, in condition to be trimmed to A provide a unit of predetermined resistance and to be mounted upon a suitable dielectric base.

A further object resides in the creation of a resistance unit of the general type set forth in the foregoing objects in which the finished unit presents a hard, glassy, non-frictional surface substantially impervious to wear; in which units of substantially identical current-resisting capacity may be produced; in which the said current-resisting capacity of an individual unit, as well as the capacities of various portions of said unit,

a may be predetermined and maintained within very low limits of tolerance; and in which the unit is not aifected by moisture. O

Other objects and advantages will become apparent in the following description and from the accompanying drawing, in which:

Figure 1 is a perspective view of a mould of suitable shape for use in the production of a resistance unit according to the invention.

Fig. 2 is a transverse cross-section of the mould shown in Fig. 1.

' Fig. 3 is a view similar to Fig. 2 showing one step of the process.

Fig. 4 is a face view of a sheet of moulded material after' it has been removed from the mould and illustrates one form or resistor element which may be formed therefrom.

Figs. 5, 6- and. fi illustrate modified forms of resistors. I

Fig. '7 is a perspective view of a modified form of mould by which a formed resistor element may be produced. n

Fig. 8 is a face View of a resistor element after it has been Fig. 'I.

Fig. 9 is a cross section of a resistor element of varying thicknesses mounted on a dielectric base.

Fig. 10 is a transverse section of a resistor of 6 constant thickness and is taken on the lines I il-i 0 of Fig. 6. Mr

In accomplishing the objects of the present invention, the current conducting element through which current fiows, is formed of finely divided or 10 comminuted particles of a material which has relativelylow electrical conductivity. The particles of material are mixed with a suitable carrying agent or liquid to form a paste-like or plastic mass capable of being worked into a desired 15 shape. A mould is generally used to define the shape. After the mass has been worked or moulded into shape, a sheet of material, which preferably has the property of absorbing the carrying liquid, is applied to the mass which is then 20 allowed to dry. In so doing, the mass adheres strongly to the sheet, which for convenience may be termed the carrier sheet, and the dried mass may then be mounted on a suitable dielectric base or otherwise finished.

More particularly, the resistance material which is preferably employed is graphite in a finely divided or comminuted form. The graphite particles are mixed with a suitable carrying or suspending liquid, of which water, ammonia 80 and. A gelatin or mixtures thereof are characteristic'examples, to produce a smooth, thick, heavy paste-like or plastic mass. The mass' should be entirely free i'rdm lumps of material and of such consistency that it may be readily worked yet does 35 not contain an excess amount of carrying liquid.

It should be understood that while graphite is chosen as an illustration of a suitable resistance material, and that the present invention will be removed from the mould shown in discussed in connection with the use of graphite, 40

the invention contemplates the use of many materials other than graphite and of carrying liquids other than water or ammonia and gelatin.

The graphite paste is shaped toform the resistor element of the unit and the most'prei'erable manner of shaping is by working the paste into a mould. By the term resistor element, or simply resistor, is meant that part of the unit through which current flows and which oflers 5 resistance to such flow. Obviously, the size and shape of the mould will be determined by the character or the resistor to-be produced. Thus, in one form, the mould (see Fig. 7) may comprise a plate Ii having an arcuate or ring-shaped 65 groove I2 therein which preferably is interrupted as at l3.

The plate is preferably formed of metal so that it may be readily maintained at a uniformly low temperature in order to facilitate the removal of the moulded material therefrom. It has been found that the most desirable results are obtained when the mould is maintained at a temperature slightly greater than average'room temperature and less than l50 F. The groove may have a definite constant depth, or the depth may vary gradually from one end of the groove to the other indicated herein as being from the end M to the end Hi. The graduated groove produces a unit, in which the resistance is graduated per unit of length.

In another form, the mould plate [6 (see Figs. 1 and 2) presents a straight groove I! of substantial width and of any length adapted to produce a sheet of resistance material from which resistors of various shapesand sizes may afterwards be easily formed. This form is probably the most desirable from a commercial standpoint since it permits quantity production at a very low cost. As in the case of the previously described mould, the groove may be of constant or variable depth. Preferably, the corners at the bottom of the groove are'slightly rounded so that the exposed corners of the finished resistor will be slightly arcuate to prevent chipping thereof.

It will be evident that the graphite paste may be readily applied to the mould, as shown at l8 (Fig. 3), care being necessary only to make sure that the mould is completely and uniformly filled. Preferably, a blunt instrument is employed to remove excess paste from the mould by drawing the instrument across the surface thereof with the instrument slidingly engaging the surface of the mould on either side of the groove. Removing the surplus material in this fashion tends to compress, or pack, the material in the mould thereby insuring that the resistor will be of uniform density throughout.

The next step of the process involves the provisionof what may be termed a carrier for the resistor. This carrier supports and reinforces the resistor while subsequent steps of the process are being performed and is applied to the resistor while the resistor is yet in the mould. Preferably, the carrier is' capable of absorbing a substantial amount of the liquid with which the graphite is moistened, is flexible, porous, has relatively great tensile strength and may be easily cut. It has been found that thin sheets of loosely matted or woven fibres are eminently suitable for this purpose.

In practice a sheet I9 (Fig. 3) of this material is applied to the exposed surface of the graphite paste in the mould while the paste is still damp and preferably immediately after the paste has been placed in the mould. The liquid-absorbing property of the thin sheet causes the sheet to cling or adhere to the moist surface and as the paste dries to become intimately attached thereto. Consequently, when the paste has dried, the moulded resistor may be lifted from the mould by the carrier sheet. Of course, other methods .and means may be employed in securing the carrier sheet or its equivalent to the resistor either before or after it has dried, but the instant method is advantageous because of its simplicity and effectiveness and because the porous, absorbent cedures may be followed depending upon the parlike.

ticular type of unit to be produced. Although the resistor, as supported by the carrier sheet, (see FigsA and 8) functions satisfactorily as a resistance unit, it is generally more practical to permanently mount the resistor on a rigid supporting base formedof some suitable dielectric material. Where the mould is formed to produce a resistor in its ultimate shape, as is the case of the resistor shown in Fig. 8, the preferred manner of mounting is to impress or embed the resistor by pressure in a. dielectric base 20 (Figs. 5, 6 and 9) formed of a somewhat compressible material such as bakelite, insulating fibre or the The term bakelite is used in its generic sense to designate a phenol condensation product either in its cured or uncured condition. If the product is cured, pressure will embed the resistor in, the base while if the base material is one containing or impregnated with an uncured product, the embedding operation occurs while the product is being cured in the usual manner by the application of heat and pressure. resistors may be pressed into a sheet of base ma terial by one operation, after which the excess base material may be trimmed away to form completed resistance units of a desired shape.

If, however, the resistors are produced in sheet form, several methods of finishing the units are possible. For example, annular resistors may be cut from the sheet as indicated at A in Fig. 4. Usually it will be most practical to provide a master die for cutting like resistors from the sheets. Thus, individual resistors of identical sizeand shape may be produced, each of which will have the same current conducting capacity, within very narrow limits of tolerance. These individual units may then be pressed into a dielectric base in the manner described.

Another method of handling the sheet resistor is to impress an entire sheet, such as that shown in Fig. 4, in a dielectric base after which the sheet is scored or otherwise cut through, as at 20*, to separate the resistor element proper from the remaining portions of the sheet. Resistors of peculiar or irregular shape and conformation, such as the spiral shapedresistor 2| (Fig. 5) or the zigzag shaped resistor 22 (Fig. 6) may be easily produced in this manner. Or a compact resistor 22 (see Fig.6) of great capacity may be formed by providing transverse scores 20 ex- A large number of 1 tending partially across the sheet alternately from opposite sides thereof. This unit is shown (Fig. 10) as being of constant thickness. The scores 20 and 20 must be of sufiicient depth and width to separate or set-off the resistor from the remaining portions 23 of the sheet so that, in the case of the resistors shown in Figs. 5 and6, the outside portions are insulated from the resistor and in the resistor 22 short circuiting between adjacent parts of the. resistor is prevented.

From the foregoing it will be apparent that a novel resistance unit has been produced by an efficient process. The graphite resistor, after moulding and drying, is of uniform consistency throughout its mass which insures that the resistance per unit of cross-sectional area will be constant. Moreover, the cross-sectional area at any point along the length of the resistor may be precisely calculated to allow the current resisting capacity per unit of length to vary according to a prearranged plan. Therefore, by varying the thickness of different portions of the graphite sheet (Figs. 3 and 4), resistance units of various types may be produced, as for example, those-embodying resistors sometimes required in connection with radio receiving set circuits, in which the resistance per unit of length gradually increases to a certain point and then decreases either at a comparable or at an entirely different rate per unit.

The resistor A (Fig. 4) is illustrative of one form wherein the resistance varies per unit of length. This resistor is cut from a sheet having a cross section comprising a relatively thin portion B, a relatively thick portion C, and an intermediate graduated portion D. The resistor is so formed from the sheet that one end thereof is fashioned from the thick portion C .of the sheet while the other end is cut from the graduated portion D. The width of the resistor also varies through its length to increase or decrease the cross-sectional area. As a result, a resistor is provided in which the part indicated at E has one current resisting capacity, the part F a higher capacity, the part G av much lower capacity, and the part H a capacitywhich approximates that of the part E.

As an additional feature, the moulded and dried graphite is very hard and presents a smooth surface for contact with a wiper shoe or other contact member, which surface is substantially impervious to War, moisture, or similar deleterious actions which tend to cause failure of resistors.

While the invention is susceptible of various modifications and alternative constructions, I

have shown in'the drawings and will herein describe in detail the preferred embodiment, but it is to be understood that I do not thereby intend to limit the invention to the specific form disclosed, but intend tocover all modifications and alternative constructions falling within the spirit and scope of the invention as expressed in the appended claims.

I claim as my invention:

\ 1. A process for manufacturing resistance units which includes the steps of forming a moist mass of comminuted resistance material into a desired shape, applying a sheet of moisture absorbing material to said mass and allowing said mass to dry thereby causing said mass of particles to adhere to said sheet forming a unitary structure.

2. A process for manufacturing resistance units which includes the steps of working a plastic mass of comminuted graphite into a mould of predetermined shape, applying a sheet of absorbent material to the exposed surface of said graphite mass to cause said mass to adhere to said sheet, drying said mass, and removing. said mass from the mould while it adheres to the sheet.

3.. A process for manufacturing resistance units which includes the steps of working a plastic mass of comminuted graphite into a mould of predetermined shape, applying a sheet of absorbent material to the exposed surface of said'graphite mass to cause said mass to adhere to said sheet, drying said mass, removing said mass from the mould while it adheres to the sheet, and mounting said moulded mass on a dielectric base.

4. A process for manufacturing resistance units which includes the steps of working a plastic mass of comminuted graphite into a mould of predetermined shape, applying a sheet of absorbent material to the exposed surface of said graphite mass to cause said mass to adhere to said sheet, drying said mass, "removing said mass from'the mould while it adheres to the sheet, and impressing said moulded mass in a dielectric base by pressure.

5. A process for manufacturing resistance units which includes the steps of workinga plastic mass of comminuted graphite into a mould of predetermined shape, applying a sheet of absorbent ma terial to the exposed surface of said graphite mass to cause said mass to adhere to said sheet, drying said mass, removing said mass from the mould while it adheres to the sheet, impressing said moulded mass in a dielectric base by pressure, and defining the resistance unit by cutting away certain portions of said inass in accordance with a prearranged plan to leave a resulting unit of a calculated current resisting capacity.

6 The herein described method of forming an electric unit of the character described which consists of molding a measured amount of electrically conductive material to desired shape and cross section, impressing the same directly upon a sheet of tissue paper, applying the sheet of tissue paper to a dielectric base and applying pressure thereto.

7. A process for manufacturing resistance units which includes the steps of working a plastic mass of comminuted graphite into a mould of predetermined shape, applyingasheet of absorbent material to the exposed surface of said graphite mass to cause said mass to adhere to said sheet, and

, removing said-mass from the mould while it adheres to the sheet.

8. A process for manufacturing resistanceunits which includes the steps of working a plastic mass of comminuted graphite into a mould of predetermined shape, applying a sheet of absorbent material to the exposed surface of said graphite mass to cause said mass to adhere to said sheet, removing said mass from the mould while it adheres to the sheet, and impressing said moulded mass in a dielectric base by pressure.

9. A process for manufacturing resistance units, which comprises forming a plastic mass of comminuted conductive material in a mould of predetermined shape, applying a carrier of absorbent material to the exposed surface of said mass to cause said mass to adhere to said carrier, and removing said mass from the mould while it adheres to the carrier.

GEORGE F. MAGDZIARZ. 

